Photoelectrocatalytic reduction of CO2 using TiO2-based catalysts synthesized by supercritical fluid technology

This work investigates the photoelectrocatalytic reduction of CO 2 (PER) in a PEM-type cell with a large electrode surface area (25 cm 2 ) equipped with gas diffusion electrodes (GDEs), employing a photoanode-dark cathode configuration, with an intermediate electrolyte layer between the cathodic GDE and the proton exchange membrane. Advanced TiO 2 -based photoelectrocatalysts (TiO 2 /CuO and TiO 2 -CNT) were synthesized via a one-step supercritical fluid process and compared with a commercial TiO 2 catalyst (P25) as photoanode for the CO 2 PER. The structural characterization confirmed the formation of nanostructured materials with dominant TiO 2 anatase phase and well-dispersed copper oxides. Photoelectrocatalytic tests under simulated solar illumination revealed that light irradiation significantly enhanced current intensity registered in the cell at constant applied voltage. Among the materials studied, TiO 2 /CuO demonstrated the highest performance, achieving CO 2 conversion rates up to 1.3 mmol CO 2 h -1 , at least three times higher than those of other catalysts studied. Formic acid and CO were the main reduction products obtained. The superior performance of TiO 2 /CuO was attributed to its enhanced photoelectrocatalytic activity toward the oxygen evolution reaction (OER), efficient charge transfer and favourable mass transport properties. These results establish TiO 2 /CuO as a promising photoanode material for CO 2 photoelectroreduction and contribute to advancing sustainable pathways for CO 2 utilization.